The present invention relates to a method of continuously separating a mixture which contains phenols, water and methanol into three separate effluent streams using a single distillation column.
Generally known methods of separating each component from a mixture containing phenols, water and methanol include the following:
(1) A method comprising distilling off water and methanol from the top of a first distillation column and recovering phenols from the bottom of the column, and then separating water from methanol by a second distillation column (Japanese Patent Laid-open No. 63-188636, etc); and
(2) A method comprising separating methanol by distillation and then separating the phenols and water by liquid-liquid phase separation.
However, method (1) has problems in that at least two distillation columns are required, and in that since water is distilled off from the top of the first column, a great deal of energy is required for evaporating the water.
The method (2) has a problem in that the phenols separated must be dehydrated since the phenols stream obtained by two-phase separation contains large quantities of water because water is highly soluble in phenols.
On the other hand, a continuous distillation method with side-stream drag, which is termed a "side cut method", is employed in the field of petroleum refining and for separating small quantities of impurities, high-purity fractions and the like. However, there are extremely few cases of this method being employed for mixtures containing phenols, methanol, water and the like. A known case using this method is only one in which a mixture containing four components including anisole, methanol, water and phenols is distilled, and a side-stream containing methanol/water and anisole is dragged from the enriching section of the distillation column, and then subjected to oil/water phase separation to obtain anisole (Japanese Patent Publication No. 3-20373).